Tim van Iersel

Adds the rel=”ugc” attribute value to links in comments and author URLs. This way the search engines will know that the links in the are added by users (User Generated Content).
Currently the plugins adds the value ugc after the nofollow value. Not all SEO tools and search engines are up-to-date and actively supporting the new attribute values.
This plugin won’t get further updates as WordPress 5.3 has the exact same attribute values implemented (nofollow, ugc).

WP UGC Comments

Adds the "ugc" value to the rel attribute for all links in comments and the author URLs.

helmanbudianto

Stackla is a social content marketing platform used by hundreds of global brands, agencies, media companies, and nonprofits to discover, curate and publish the best content from the social web. Stackla’s WordPress plugin allows you to display social media content and display via a Stackla widget directly on a Post or a Page.
Shortcode
<blockquote>
[stackla]
</blockquote>

Stackla

Integrate social media content directly into your WordPress websites.

WP UGC Comments vs Stackla